Preliminary design considerations for a rockbed/floor space-heating system

Abstract

A solar energy house space-heating system, in which thermal energy is transferred by conduction through a concrete floor from a subfloor rockbed, is considered from the aspect of the store being able to maintain comfort conditions with no further solar energy input. The rate of decay of temperature variations along the floor is also considered. The study uses a solution of the two-dimensional diffusion equation for a composite slab subjected to a sudden change in environment: the pertinent details of the solution are given. The study shows that the interaction between the collectors, store and load is more critical in this system than in a conventional active solar-heating system. It is possible for the floor-heating system to have a storage capability which would give a system performance comparable to that for a conventional system in mild climates, but the system is less suited to more severe climates. If a phase-change material is used in the porous bed, then the bed can be very thin, but a high pressure drop and complex subfloor ductwork would need to be avoided. For thicker beds, it would be advantageous to encourage free convection within them.